Zod headed to Earth after picking up a distress call, presumably activated (possibly unknowingly) by Clark or Jor-El's AI going by Zod's dialogue of picking it after 30 years or so of faffing around in space.

It also wasn't a surprise to Zod that Kal-El was there lending credence to the idea that the call was sent by Clark himself.

Given Jor-El's plan, it makes sense that he would want to summon any Kryptonian survivors once his son had paved the way for them to be accepted. He either failed to anticipate that Zod would escape the Phantom Zone, or failed to anticipate that Zod would reject his plan in favor of planetary genocide as a matter of convenience.